Intramolecular cross-linked hemoglobins containing a covalent bridge between the beta chains will be synthesized. Phosphorylated dialdehydes will be prepared and will be condensed with human stroma-free hemoglobin to yield Schiff bases which will be reduced to form a covalent bridge between the beta chains of hemoglobin. It is expected that the bridged hemoglobin will be retained in the circulation because it cannot dissociate into dimers, in which form the unmodified hemoglobin is excreted into the urine. The bridged hemoglobin solution should deliver oxygen to tissues in the presence of red blood cells because its affinity for oxygen is much lower than that of unmodified hemoglobin. The delivery of oxygen by the bridged hemoglobins will be evaluated with an isolated, perfused rat brain preparation and by infusion into intact animals. Retention in the circulation, effects on vital functions and on blood clotting and blood platelets will be evaluated in intact animals.